The present invention relates to a method of and apparatus for controlling the operation of an internal combustion engine which is equipped with a digital calculation unit.
A digital arithmetic unit such as microcomputer has frequently been employed as an arithmetic unit for internal combustion engines of the type which detect various data representing the operating conditions of the internal combustion engine, such as running speed, amount of air intake, pneumatic pressure of the intake manifold, air-fuel ratio condition, water temperature, temperature of the air intake, battery voltage, opening degree of a throttle valve and atmospheric pressure, and which performs predetermined arithmetic calculations based upon the detected data, in order to control various actuators in the ignition system, fuel feeding system, and air-fuel ratio control system. The digital arithmetic unit of this type stores various data for use in the arithmetic calculation (such as arithmetic constants, reference values, coefficients, and characteristic data used for the arithmetic calculation), in a fixed storage such as read-only memory (ROM) which holds the data even after the power supply of the engine has been turned off.
With the conventional art, however, a problem develops when it is required to change the data used in the arithmetic calculation and stored in the ROM as a result of a design modification of the engine or re-adjustment during the manufacturing steps.
When the ROM is a masked ROM, it is necessary to replace not only the ROM to change the stored data but also to change the mask patterns during the steps of manufacturing the ROM. To change the data, therefore, a period of at least two to three months and tremendous expense are required.
Even when there is used a programmable ROM (PROM) such as a fusing-type ROM which enables the data to be written in only once, the ROM must be replaced to write the new data and requires considerable expense.
The data can be quickly changed if there is used an erasable programmable ROM (EPROM) which permits the stored contents to be erased. The EPROM, however, is expensive, and presents a probability that the stored content may be extinguished with the lapse of time. The EPROM, therefore, has a problem with regard to reliability.
If the data is generated by a discrete circuit, the data can be changed simply by changing the circuit constant of the discrete circuit. This, however, causes the discrete portion to become complex, while presenting such problems as decreased reliability that may be caused by faults and defects, cumbersome adjustment, and increased manufacturing cost.